1. Field of the Invention
The present invention relates to a thermal head manufacturing method.
2. Description of the Related Art
There have been conventionally known thermal heads for use in thermal printers, which are often mounted to a small-sized information device terminal, typically, a small-sized handy terminal. A thermal head in a thermal printer prints an image on a heat-sensitive recording medium by selectively driving some of a plurality of heating elements based on printing data (see, for example, JP 2007-83532 A).
One way to improve the efficiency of a thermal head is to form a hollow portion (hollow heat insulating layer) on a layer below a heating portion of a heating resistor. Forming the hollow heat insulating layer on a layer below the heating portion makes the amount of upward-transferred heat, which is heat generated by the heating resistor and transferred to a wear-resistant layer above the heating portion, larger than the amount of downward-transferred heat, which is heat generated by the heating resistor and transferred to a heat storage layer below the heating portion, thus enhancing the efficiency of energy required during printing.
In such a thermal head that has a hollow structure, expanding the hollow portion by making thin the heat storage layer which supports the heating resistor enhances the heat insulation performance and improves the heating efficiency. On the other hand, making the heat storage layer thin reduces the strength for supporting the heating resistor. It is therefore important to determine a heat storage layer thickness that ensures reliability and durability while maintaining the heating efficiency.
JP 2007-83532 A describes a thermal head manufacturing method in which a thin glass plate that is thick enough for easy handling is bonded to a substrate, instead of a very thin glass plate which makes manufacture and handling difficult, and then the thin glass plate is processed by etching, polishing, or the like to form a very thin heat storage layer to a desired thickness.
However, considering the etching process capability and the ease of manufacture and handling, forming a heat storage layer of a desired thickness with precision by a conventional thermal head manufacturing method requires the substrate size to be smaller. This gives rise to a problem in that the size of a thermal head to be manufactured is limited. Another problem is that, in the case where a plurality of thermal heads are to be formed from a substrate, fewer thermal heads are obtained, which means lowered productivity and increased cost.